Vacuum-tube circuits and method of operating them



R. C. MATHES AND H. S READ.

VACUUM TUBE CIRCUITS AND METHOD OF OPERATING THEM.

APPLICATION FILED MAY 9. 1919.

1,426,755, I PatentedAug. 22,1922

fly W 42797.

Matteo am s PATENT castes.

Bonner c. MATHES, or New roan, N. *z'.,

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NEW JERSEY, ASSIGNORS T0 WESTERN ELECTRIC COMPANY, INCORPORATED, @E NEWYORK, N. Y., A CORPORATION OF NEW Y0.

VACUUM-TUBE CIRCUITS ANIID METHOD 01E OPERATING TEETH.

;ments in Vacuum-Tube Circuits and Methods of -Operating Them, of whichthe fol- ,lowing is a full, clear, concise, and exact 1 description.

This, invention relates to vacuum tube circuits, and more particularlyto multistage amplifier circuits in which vacuum tubes are employed inthe various stages. 7

It is well known'in the art that a vacuum tube of the three electrodetype, for example, will reproduce in amplified form in its outputcircuit impulses impressed upon its input terminals, and that theamplified impulses may be impressed onthe input terminals of othertubesto ive any desired degree of amplification. hen such a multisageamplifier is employed to amplify low frequency impulses, it is generallypreferableto have a direct coupllng instead of an inductive couplingbetween'stages in .order that the low frequency impulses will beaccurately reproduced by the amplifiers. But when such a direct couplingis employed considerable difliculty is experienced when i signals arebeing received from preventing the output-current of one tube from soaffecting the potential applied to the control electrode of a secondtubethat the second tube is either blocked or has its amplifying actiondestroyed on account of its control electrode becoming too positive ortoo negative. In accordance withth'is invention, it has been found thatthe operation of such a multisage amplifier set is considerably improvedby providing adjustable sourcesof potential for the control electrodesof the tubes, and'by providing switching means between the stageswhereby the output current of each tube may be given its proper value byadjusting the normal source of potential for its control electrodeindependently of this-influence of the output cur.- rent of thepreceding tube. This invention will be more fully understood byreference to the following detailed description taken n connection withthe accompanying draw- I Specification of Letters Patent. P m t fl Aug;22 922 Application filed may 9, 1919. serial No. 295,820.

ng which shows one embodiment of this invention in connection with athree stage amplifier set.

Referring to the drawing, 3, 4 and 5 are vacuum tube amplifiers havingfilaments 6, 7 and 8, anodes 9, 10 and 11 and control electrodes 12, 13and 14 respectively. Each of these filaments may have a resistance ofthe order of 4 ohms. 16 is a source of heating current for thefilaments, and it is to be noted that starting with the positive pole ofthe battery 16, the heating current goes through the filament 8, 6 and 7in the order named. ()utput circuit current for tube 3 is supplied frombattery 18, while the output circuits of tubes 4 and .5 are suppliedfrom battery'19. A source of potential for the grid 12 is secured by theTR drop in that part of resistance 20 which is included 1n circuitbetweenthe grid and the filament 6. An adjustable contact 21 is providedfor varying the amount of the potential applied to the grid. Thisresistance 20 which @115 EAST GRANGE, v

in one case had a value of 170 ohms, is in the heating circuit for thefilaments and is in shunt to filament 7 and a small resistance 22, thefunction of which will be described "later.

The input circuit for tube 3 may be traced through high resistance 23,contact 21, a portion of resistance 20 to filament 6. The output circuitfor tube 3 may be traced from the anode 9, jack 25, high resistance 26,a source of voltage 18 and either through'resistance 20 orresistance 22and filament 7 to filament 6.

tial of these two sources and the value of the IR drop in resistance 26and may beregulated by means of contact 30. Resistance 22 will generallybe ofsuch a small value that the IR drop in it due to battery 18 may beneglected in this instance. When switch 27 is moved to contact 32 theinput circuit of tube 4 is disconnected from the output circuit of tube3 and contains only the small resistance 22. Therefore with the switch27 on contact 32 the potential of the rid 13 is determined efiectivelyby the TR rop in resistance 22, the effect of the high shunt resistance20 being negligible in this case. The output circuit for tube 4 may betraced from anode 10, jack 35, resistance 36, source of voltage 19 tothe cathode 7.

The input circuit for tube 5 includes source of voltage 37, switch 38,contact 39, jack 35, resistance 36, source of voltage 19 and thefilament heating circuit to cathode 8, so that the potential of the grid14 would depend upon the resultant potential of the oppositely poledsources 19 and 37 and the drop in potential in resistance 36; theresultant potential of grid 14 may be regulated by means of adjustablecontact 40. However, when switch 38 is moved to contact 41 the inputcircuit for tube 5 is disconnected from the output circuit of tube 4 andcontains only the source of voltage 37. The output circuit for-tube 5includes the jack 42, a receiving device such as an oscillograph 43,battery 19 and the filament heating circuit to filament 8.

The manner in which such an amplifier set may be adjusted for properworking may be explained as follows. A measuring instrumentshould beconnected in the output circuit of tube 3 by means of jack 25, and thevalue of the output current adjusted to its best working value byvarying the potential of the grid 12 through adjustment of contact 21.Preceding this operation switch 27 should be moved to contact 32, inorder to prevent battery 18 from supplying current to the input circuitof tube 4. If the battery 18 were allowed to supply current to tube 4,the adjustment of tube 3 might be appreciably affected thereby.

In order to adjust tube 4 for best working operation, switch 27 shouldbe kept on contact 32, thereby disconnecting tube 3 from the inputcircuit of tube 4, and switch 38'should be moved to contact 41 in orderto prevent battery'19 from supplying current to the input circuit oftube 5. The potential of grid 13 is determined efiectively by the IRdrop in resistance 22, which should be of such a value as to give theproper space current between the cathode and anode of tube 4, and ofsuch a value as would maintain the grid always negative when normalsignalling currents are passing through the amplifier. In one case,resistance 22 had a value of one ohm. The measuring instrument should beinserted in the output circuit of tube 4 by means of the jack 35 and thevalue of the current noted. Switch 27 should then be moved to contact 28and the value of the source of voltage 29 adjusted until the spacecurrent for tube 4 has the same value it had with switch 27 on contact32. In order to get this adjustment accurately, it may be necessary toadjust slightly contact 21 on resistance 20, which will not changeappreciably the output current of tube 3, but will produce appreciablechanges in the output current of tube 4 due to the amplifying power ofthe tube. After these adjustments the potential relation of grid 13 tofilament 7 is the same as was initially determined by the IR drop inresistance 22.

In a similar manner switch 38 should be moved to contact 41 and thevalue of source of voltage 37 adjusted to give the normal grid potentialto tube 5. For example, if tube 4 in normal operation produces a maximumchange in the potential of grid 14 of 20 volts, battery 37 should beadjusted to a value slightly greater, say 22 I volts, in order tomaintain grid 14 always negative. The value of the space current of tube5 for this setting should be noted by the instrument connected in theoutput circuit through jack 42. The switch 38 should then be moved tocontact 39 and the effective value of battery 37 adjusted until thespace current has the same value it had with switch 38 on contact 41.The set is then read to be employed as the amplifier for signa simpressed across the terminals of resistance 23."

It is obvious that various changes may be made in the circuitarrangement above described without departing in any wise from thespirit of this invention as defined in the appended claims.

What is claimed is:

1. A plurality of "acuum tubes each having an input circuit and anoutput circuit, the output circuit of one of said tubes being associatedwith the input circuit of a second of said tubes, each of said tubescomprising a cathode and a control electrode, means for supplyingcurrent to said cathodes, and means for supplying a difi'erence ofpotential between the cathode and a control electrode of one of saidtubes, said means comprising the potential drop in a resistanceconnected in shunt to a cathode of a succeeding tube.

2. A plurality of vacuum tubes'each having a cathode, an input circuitand an output circuit, the output circuit of one tube eing associatedwith the input circuit of another of said tubes, and a resistance inshunt to one 0 said cathodes, said resistance being included in theinput circuit of a tube preceding the tube having the shunted cathode.

3. A plurality of vacuum tubes each having a cathode, an input circuitand an output circuit, the output circuit of one vacuum eing associatedwith the input circuit of another of said vacuum tubes, the inputcirouit of one of said tubes including the cathode of a succeeding tube.

4. A plurality of vacuum tubes each having a cathode, a controlelectrode, an inmamas i put circuit and an output circuit, the outputcircuit of one or said tubes being associated with the input circuit ofanother of said tubes, means for supplying current to said cathodes, andmeans for applying p0 tential to one'of said control electrodes com--prising the drop in potential across the terminals of a cathode of asucceeding tube.

5. The combination of a plurality of vacuum tubes connected in tandem,each of said vacuum tubes having an input circuit and a filamentaryelectrode, the input circuit of one of said tubes including saidelectrode of a succeeding tube.

6. The combination with a vacuum tube having a control electrode and afilament, of a source of current for heating said filament, a resistancetraversed by current from said source, a source of voltage for saidcontrol electrode, switching means for connecting at times said controlelectrode with said source of voltage, and at other times for connectingsaid electrode to thatterminal of said resistance which is electricallyremote from said filament.

g 7. Themethod of operating a plurality of vacuum tubes in which theoutput current at one of said tubes controls the input potentialappliedjtoa second tube, said first and said second tubes each having acontrol electrode and a cathode, which method comprises controlling thepotential of the control electrode of said first tube in accordance withthe potential diitference across the terminals of the cathode of saidsecond tube.

8. The method of operating a plurality of vacuum tubes connected intandem, each of a plurality of said tubes comprising a control electrodeand a cathode, which method comprises controlling the potentialdifierence between the control electrode and the cathode of one of saidtubes in accordance with the potential or an electrode of a succeedingtube.

9. A multi-stage vacuum tube system comprising several vacuum tubes,each having a cathode, a source of voltage, and connections to saidsource for heating said cathodes whereby the otential of one of saidcathodes as regar s said source is intermediate the potential of twosucceeding cathodes.

of said tubes, said testing means comprising means for inserting ameasuring instrument in circuit with the output electrode of onecit-said tubes, and means for dlsconnecting the input electrode of thetube under test from the output electrode of the preceding tube. 1 v

11. A vacuum tube system comprising a plurality'ot vacuum tubesconnected in tandem, each of said tubes having an input electrode and anoutput electrode, means for providing a direct current path between theinput electrode of one of said tubes and the output electrode of anotherof said tubes, and means for testing the operation of one of said tubes,said testing means comprising means for inserting a measuring instrumentin circuit with the output electrode of one of said tubes, and means fordisconnecting the output electrode of the tube under test frgm'the inputelectrode of the succeeding tu e.

12. A vacuum tube system comprising a plurality of vacuum tubesconnected in tandem, each of said tubes having an input electrode and anoutput electrode, means for providing a direct current path between thelnput electrode" of one tube and the output electrode of another of saidtubes, and means for testing the operation of one of said tubes, saidtesting means comprising means for inserting a measuring instrument incmcuit with the output electrode of one of said tubes, means fordisconnecting the input electrode of the tube under test from the outputelectrode of the preceding tube, and means for disconnecting the outputelectrode of the tube under test from the input electrode of'thesucceeding tube.

13. vacuum tube system comprising a plurality of vacuum tubes connectedin tanice dem, each of said tubes having an input electrode and anoutput electrode, an input circult and an output circuit, means forprores viding a direct current path between the input electrode of oneof said tubes and the output electrode of another of said tubes,

means for supplying current to said output circuits, and means fortesting the operation 9 0 n or one of sa1d tubes, said testing meanscomprising means for preventing the output cir- 'cuit current of thepreceding tube from infiuencing the potential of the control eleetrodeot the tube under test, and means for preventing the output circuitcurrent of the tube under test from influencing the potential of thecontrol electrode of the succeeding tube. V

it. A vacuum tube system comprising a plurality of vacuum tubesconnected in tandem, each of said tubes having an input electrode and anoutput electrode, an input circuit and an output circuit, means forproviding a direct current path between the in put electrode of one ofsaid tubes and the output electrode of another of said tubes,

means for supplying current to said output circuits, and means fortestmgthe operation of one of said tubes, said testing means com= tricalcharacteristics of said tube and another of said sources being dependenton said 10 electrical characteristics.

In witness whereofl we hereunto subscribe our names this 7th day of MayA. 1)., 1919.

ROBERT C. MATHES. HARRY S. READ.

